Uncomplicated load-adapting electrosurgical cutting generator

ABSTRACT

A high frequency signal for cutting human tissue is generated by common-emitter configured oscillator circuit that is adapted to maintain the cutting signal relatively constant in spite of impedance variations in the load caused by variations in the conduction of the tissue being cut.

BACKGROUND OF THE INVENTION

The present invention relates generally to improvements in cuttingsignal generators in electrosurgical devices, and more particularlypertains to new and improved oscillator circuitry utilized forgenerating high frequency cutting signals.

In the field of electrosurgical devices, it has been the practice toemploy various types of electrosurgical generators suitable forgenerating cutting and coagulation currents. In some cases, the currentsare provided by separate generators, one generator providing a cuttingcurrent and the other generator providing a coagulation current. Inother cases, a single generator is utilized to provide both a cuttingand coagulating current, or a combination of such currents. These priorart electrosurgical instruments, whether they used separate signalgenerators or one signal generator for producing the various types ofsignals required, either ignore the problem of the patient acting as avarying impedance load, or compensate for it by expensive andcomplicated means.

SUMMARY OF THE INVENTION

An object of this invention is to provide an electrosurgical device thatprovides a relatively constant tissue cutting signal, in spite ofimpedance changes in the load.

This object and the general purpose of this invention are accomplishedby providing a transistor regenerative feedback oscillator-amplifierthat has a load-coupling transformer in the collector circuit along witha feedback coupling winding to provide regenerative feedback to the basecircuit which contains the frequency determining elements. The outputsignal from this oscillator-amplifier is applied to human tissue forcutting purposes.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as it becomes better understood by referenceto the following detailed description when considered in conjunctionwith the accompanying drawings, in which, like reference numeralsdesignate like parts throughout the figures thereof and wherein:

FIG. 1 is a block diagram illustration of a typical electrosurgicaldevice.

FIG. 2 is a circuit diagram of the preferred embodiment of the cuttingsignal generator of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to FIG. 1, the organization of an electrosurgical devicethat could utilize the cutting signal generator of the present inventionis illustrated. A power supply 11 supplies DC power to a switchingdevice 15 by way of cable 13. The switching device 15 may bemechanically or electromechanically actuated and is intercoupledelectromechanically 31 with a switching device 29 at the output of acoagulating signal generator 21 and a cutting signal generator 23.Switching device 15 selectively supplies energy from the power supply tothe coagulating signal generator 21 over cable 17.

The coagulating signal generator 21 may be a spark-gap oscillator thatsupplies high current, high frequency, damped oscillations over cable 25to switching device 29. Switching device 29 may contain manuallyadjustable signal controls and path selection devices to, for example,switch the coagulating signal to line 33. Line 33 is then connected to asurgical instrument. Line 39 may be connected to the grounding or"indifferent" plate, contacting the patient and acts as a return pathfor the electrosurgical signal.

If a cutting signal is desired, switching device 15 supplies DC energyfrom the power supply 11 to the cutting signal generator 23 by way ofcable 19. The cutting signal generator 23, as will be more fullyexplained hereinafter, is a medium frequency, high poweroscillator-amplifier that generates a continuous signal. This signal issupplied to switching device 29 over cable 29. Switching device 29connects this signal to a cutting terminal 35 which is connected to asurgical instrument (not shown). Electrosurgical devices such as,illustrated by FIG. 1, are well known in the prior art.

The cutting signal generator 23, illustrated in FIG. 2, is uniquelydesigned to accommodate itself to the varying load conditions presentedby the human body. The load 59 connected across the cutting signalgenerator output lines 27a, 27b may go from infinite impedance to zeroimpedance. However, practically speaking, when operating in the humanbody, the load can vary from several thousand ohms down to around 30ohms.

The cutting signal generator 23 comprises an NPN transistor amplifier 53shown to be configured in a commonemitter arrangement. The transistoramplifier is illustrated as being made up of one transistor. However, itshould be understood that as many transistors as is necessary, connectedin parallel, may be utilized to achieve the desired power output. Thetransistor amplifier 53 is connected as a regenerative feedbackoscillator by way of a feedback transformer having a primary winding 41and a secondary winding 43. Primary winding 47 of the load transformeris connected in series with the primary winding 41 of the feedbacktransformer. The secondary winding 45 of the load transformer isconnected to the load 59 over output lines 27a, 27b.

The transistor amplifier 53 is biased by a resistor 49, which keeps thecollector terminal at side 1 of resistor 49 positive with respect to thebase at side 2 of the resistor 49. It should be understood that this NPNarrangement is only exemplary and that PNP transistors may be used aswell, the biasing being rearranged appropriately.

A DC voltage from the power supply 11 is supplied to side 1 of theprimary winding 41 over line 19. The secondary winding 43 of thetransformer inversely couples the signal in the primary winding 41 tothe base of transistor 53 by way of capacitor 51. One side of thesecondary winding 43 is grounded, while the other side is connected toone side of capacitor 51.

The emitter of the transistor 53 is also grounded. The primary winding47 and secondary winding 45 couple the signal in the collector circuitof transistor 53, without inversion, to the load.

The effective inductance of the winding 43 in the feedback loop and thecapacitance of capacitor 51 in the feedback loop determine the timeconstant of the regenerative feedback oscillator circuit illustrated. Inother words, the frequency of the output signal is determined by thevalue of inductor 43 and the value of capacitor 51.

When a DC power source is supplied to terminal 1 of primary coil 41, byway of line 19, the polarity of the primary winding will be plus atterminal 1 and minus at terminal 2. The polarity of primary winding 47will be plus on top and minus on the bottom. The polarity of resistor 49will be plus at terminal 1 and minus at terminal 2. This will bias thetransistor 53 in a forward direction causing base current 63 to startflowing. When such base current starts flowing, collector current 61 andemitter current 65 will also start flowing in the direction shown by thearrows. The base current illustrated is actually electron flow. Itshould be understood that conventional current flows in a directionopposite to electron flow. This electron flow causes an expandingelectromagnetic field in primary windings 47 and 41.

The electromagnetic field caused by primary winding 41 is coupled tosecondary winding 43 which is wound to cause polarity inversion.Thereby, terminal 4 of winding 43 will be positive and terminal 3 willbe negative when terminal 1 of primary winding 41 is positive andterminal 2 is negative. As electron flow increases in the collectorcircuit of transistor 53, the current induced in secondary winding 43,as a result of the expanding electromagnetic field in winding 41, willcause a positive charge build-up on plate 1 of capacitor 51. The otherside or plate 2 of capacitor 51 will, therefore, have an increasingnegative charge. This increasing negative charge at plate 2 acts tofurther bias the transistor 53 in the forward direction, causing anincrease in base current 63, which in turn causes an increase incollector current 61 and emitter current 65.

This action will continue until the collector current 61 reaches amaximum as determined by the elements 41, 47 in the collector circuitand the transistor 53. At such time, since the current is no longerincreasing, lack of an electromagnetic flux change in the primarywinding 41 causes a lack of feedback current, by way of inductor 43 andcapacitor 51. At such time, plate 1 of capacitor 51 has reached itsmaximum positive charge, as shown by the first half cycle of wave 55.The opposite plate 2 of capacitor 51, at this time has reached itsmaximum negative charge as shown by the first half cycle of wave 56.

The capacitor 51 will start discharging through inductor 43 to ground,according to the particular time constant dictated by the values ofcapacitor 51 and inductor 43. This discharge action causes the basecurrent 63 to decrease, thereby decreasing the collector current 61 andthe emitter current 65 of transistor 53. Since the collector current isnow collapsing, the feedback coupling between primary winding 41 and thesecondary winding 43, will aid this process, causing the capacitor todischarge until the transistor 53 is driven to cut-off as exhibited bypractically zero emitter current and collector current.

At this time, plate 1 of capacitor 51 has reached its maximum negativecharge, as shown by the second half cycle of wave 53. The other plate 2of capacitor 51 has, in turn reached its maximum positive charge, asshown by the second half cycle of wave 56.

The biasing resistor 49 maintains the transistor in a forward biascondition, thereby causing base current 63 to again increase, in turnincreasing emitter current 65 and collector current 61. This actioncauses a repeat of the first half cycle, as shown by waves 55 and 56.Oscillation will continue in this manner until removal of the DC supplyfrom side 1 of the primary winding 41 of the feedback transformer.

The primary winding 47 and the secondary winding 45 couple the load 59into the collector circuit of the transistor 53. What in effect occursby this arrangement, is the load impedance of the load 59 is reflectedback into the primary 47 of the transformer so that, effectively,primary winding 47 may be replaced by the reflected impedance value ofthe load. Therefore, primary winding 47, secondary winding 45 and theload 59 can be thought of as a variable impedance in the collectorcircuit.

Bearing this in mind, it can be seen that as the value of the loadimpedance in the collector circuit of transistor 53 decreases, thecollector current will increase. Assuming that the collector current 61is in the increasing part of its cycle, a decreasing load impedance willtend to increase the collector current causing the voltage drop acrossthe primary winding 41 to become larger. This increasing voltage drop iscoupled from the primary winding 41 to the secondary winding 43, whichin turn increases the feedback signal to the capacitor 51 therebyfurther forwarding biasing the transistor 53. This increased forwardbiasing increases the base current 63, the collector current 61 and theemitter current 65. The increasing collector current will compensatecommensurately for the decreasing reflected impedance of the load tokeep the voltage across the load from swinging sharply to a value belowthe desired minimum.

Assume now that the load impedance is increasing and the collectorcurrent is in an increasing cycle. The increasing impedance will causethe collector current to decrease. This causes the voltage drop acrossthe primary winding 41 to decrease correspondingly, thereby decreasingthe feedback signal and causing the charge on capacitor 51 to decrease.This decreases the forward bias of the transistor 53 which causes adecrease in the base current 63 and a commensurate decrease in thecollector current 61. Here, the combination of a decreasing collectorcurrent with an increasing reflected load impedance keeps the voltageacross the load from swinging sharply to a value above the desiredmaximum.

Besides stabilizing the voltage swings across the load, the oscillatorof FIG. 2 controls the change in current through the load, thereby alsopreventing erratic swings in load current.

In summary, what has been disclosed is an electrosurgical device thatutilizes an uncomplicated and inexpensive oscillator-amplifier circuitfor generating tissue cutting signals. The oscillator-amplifier isdesigned to inexpensively adapt itself to impedance changes of the load.Obviously, many modifications and variations of the foregoingdisclosure, as illustrated by the preferred embodiment, are possible inlight of the above teachings. It is, therefore, to be understood thatwithin the scope of the appended claims the invention may be practicedotherwise than as specifically described.

What is claimed is:
 1. In an electrosurgical device having a powersupply, a cutting signal generator driven by said power supply, andswitching means for selecting the output signal of said generator forsupply to a varying impedance cutting electrode load, the improvementtherein being a cutting signal generator comprising:amplifier meanshaving an input and output circuit for supplying an output current inits output circuit which varies inversely with the impedance variationof said load; and means coupling the output current variation of saidamplifier means to the input circuit of said amplifier means for causingsaid amplifier means to controllably reinforce the current variation inits output circuit.
 2. The cutting signal generator of claim 1 whereinsaid coupling means include means for providing positive feedback to theinput circuit of said amplifier means.
 3. The cutting signal generatorof claim 1 wherein said amplifier means comprises a transistoramplifier.
 4. The cutting signal generator of claim 3 wherein saidtransistor amplifier comprises an NPN configured amplifier circuit. 5.The cutting signal generator of claim 4 further comprising a biasingresistor connected between the output and input circuit of said NPNtransistor.
 6. The cutting signal generator of claim 1 furthercomprising transformer means for coupling said output circuit to theload and transferring the voltage generated in the output circuit to theload.
 7. The cutting signal generator of claim 1 wherein said couplingmeans comprises a transformer inversely coupling said output circuit tosaid input circuit.
 8. The cutting signal generator of claim 7 furthercomprising a capacitor connecting said output-input coupling transformerto said input circuit, providing a desired time-constant for the cuttingsignal.
 9. In an electrosurgical device having a power supply, a cuttingsignal generator driven by said power supply, and switching means forselecting the output signal of said generator for supply to a varyingimpedance cutting electrode load, the improvement therein being acutting signal generator that maintains a relatively constant voltageacross said varying impedance cutting electrode load, said cuttingsignal generator comprising:amplifier means having an input circuit andan output circuit for amplifying the signal supplied to its inputcircuit; a first coupling transformer having a primary and a secondarywinding, said secondary winding being directly connected to said loadand said primary winding being connected in the output circuit of saidamplifier means; and a second transformer having a primary and secondarywinding, said primary winding of said second transformer being connectedto the primary winding of said first transformer and said secondarywinding of said second transformer being connected in the input circuitof said amplifier means in a manner to inversely couple a signalgenerated in the primary winding of said second transformer to the inputcircuit of said amplifier means.
 10. The electrosurgical device of claim9, further comprising a capacitor connected between the secondarywinding of said second transformer and the input circuit of saidamplifier means.
 11. The electrosurgical device of claim 10 wherein theprimary and secondary winding of said second transformer provide voltageinversion between the two windings.
 12. The electrosurgical device ofclaim 10 wherein said amplifier means comprises a transistor amplifier.13. The electrosurgical device of claim 12 wherein said transistoramplifier comprises an NPN configured amplifier circuit.